Why is the root volume usage reporting incorrectly?

In Mac OS X 10.6 and above, the Finder uses the kilo = 1000 standard when calculating file and volume sizes. However, different tools report different file sizes and volume usage, such as the Info details and Quick Look.

Watchman Monitoring uses the terminal command df when checking the root drive capacity. The kilo = 1024 standard is used by df.

Regardless of the numerical size reported, the warning is triggered based upon the percent of drive space used, which is calculated correctly.